The present invention relates to a tail tube structure of gas turbine combustor. More particularly, this invention relates to a structure for enhancing the performance of gas turbine by increasing the cooling effect in the tail tube seal, decreasing the cooling air flow to save the air consumption, and decreasing the load of the compressor.
FIG. 9 is a general structural diagram of a combustor of a gas turbine. Reference numeral 80 indicates a combustor. This combustor 80 is fixed in a casing 81. Reference numeral 82 indicates a pilot fuel nozzle. Pilot fuel to be used for ignition is supplied to the pilot fuel nozzle 82. Reference numeral 83 indicates a main fuel nozzle. A plurality of main fuel nozzles (for example eight in number) are arranged in a circle around the pilot fuel nozzle 82. Reference numeral 84 indicates an inner tube, and 85 indicates a tail tube. The inner tube 84 and the tail tube 85 guide a high temperature combustion gas 200 towards an outlet 86 of the tail tube 85 (hereafter tail tube outlet). Reference numeral 87 indicates a bypass pipe, and 88 indicates a bypass valve. The bypass valve 88 gets opened when the combustion air becomes insufficient because of the fluctuations in the load. When the bypass valve 88 gets opened, a passage is created for guiding the air in the casing 81 into the combustor 80. Reference numeral 89 indicates a seal section. This seal section 89 is provided at the peripheral end of the tail tube outlet 86 as described below. The seal section 89 is intended to seal the connection area with gas passage (alternatively the xe2x80x9cgas passxe2x80x9d) 100 of the gas turbine. A plurality of such combustors 80 (for example sixteen in number) are disposed around the rotor in the casing 81. Each combustor 80 supplies the high temperature combustion gas into the gas pass 100. This combustion gas expands in the gas pass 100 to work and rotate the rotor.
In the combustor having such constitution, the fuel from the main fuel nozzle 83 is mixed with the air sucked from around. The mixture of fuel and air is ignited by the flame of the pilot fuel from the pilot fuel nozzle 82. The mixture burns to form a high temperature combustion gas 200. The high temperature combustion gas 200 is supplied from the tail tube outlet 86 into the gas pass 100 through the inner tube 84 and tail tube 85. Since the wall of the inner tube 84 and the wall of the tail tube 85 always come in contact with the high temperature combustion gas 200, a cooling passage for passing cooling air is provided in these walls in order to cool them. Moreover, the tail tube outlet 86 is connected to the periphery of the inlet of the gas pass 100 through the seal section 89. This seal section 89 is also cooled using the cooling air.
FIG. 10 is a magnified sectional view of portion Y in FIG. 9. This figure shows a detail structure of a conventional tail tube seal. Reference numeral 89 indicates the entire seal section. A flange 86a is formed around the tail tube outlet 86. The wall of the tail tube is exposed to high temperature combustion gas 200, for example, the temperature of the gas as high as 1500 degree centigrade. However, multiple passages (not shown) for cooling air are formed in the wall of the tail tube 85, and the wall is cooled by the cooling air. Further, a groove 90 for cooling air is also formed around the tail tube outlet 86. The tail tube outlet 86 is cooled by passing the cooling air in this groove 90.
The tail tube outlet 86 is connected to the gas pass 100 through a tail tube seal 61. One end of the tail tube seal 61 has a U-shaped groove 61a. A peripheral flange 86a of the tail tube outlet 86 is fitted into this groove 61a. The other end of the tail tube seal 61 has a pi-shaped groove 61b. Flange ends 102a, 103a of an outer shroud 102 and an inner shroud 103 of a first stage stationary blade 101 in the gas pass 100 are fitted into this groove 61b, thereby sealing the connection area.
Since the tail tube seal 61 is also exposed to high temperature combustion gas 200 as mentioned above, multiple cooling holes 61c are drilled around the tail tube seal 61 in a direction which is perpendicular to the direction into which the gas flows at the inlet of the gas pass 100. High pressure air 91 flows in from around the combustor in the casing and cools the wall of the tail tube seal 61. After cooling, this air flows into the gas pass 100. The amount of cooling air required to cool the tail tube seal 61 is about 1 to 2% of the amount of compressed air discharged from the compressor.
Thus, in the tail tube seal of the conventional gas turbine combustor, air holes 61c are drilled on the periphery of the tail tube seal 61 and the tail tube seal 61 is cooled by passing cooling air 91 in the air holes 61c. The periphery of the holes 61c is cooled by passing cooling air into the holes 61c, however, the side of the groove 61b connecting to the gas pass 100 side is not cooled sufficiently by passing cooling air into the holes 61c alone. As the cooling is insufficient, the flange ends 102a, 103a towards the gas pass side expand due to thermal expansion. This thermal expansion of the flange ends 102a, 103a generates a frictional force at the contact with the groove 61b and the groove 61b is worn. Thus, the performance of the tail tube seal 61 is impaired.
Moreover, the amount of air required to cool the tail tube seal 61 is about 1 to 2% of the entire amount of compressed air discharged from the compressor. However, it is desirable that this air consumption is as little as possible, because, when the air consumption is less, the efficiency of the compressor can be improved and the performance of the gas turbine can be enhanced. Such a decrease in the air consumption was in demand but was not realized till present.
It is an object of the present invention to present a tail tube seal structure of a combustor capable of improving the cooling structure of the tail tube seal of a combustor of gas turbine, raising the cooling effect, curtailing the amount of air by cooling by a smaller amount of air, and contributing to an upgraded performance of the entire gas turbine.
According to one aspect of the present invention, the air in the casing flows in from a plurality of inclined cooling holes and flows out obliquely into the gas pass, and cools the wall contacting with the gas passage in the groove in which the flange end of the gas pass is fitted by film effect, the cooling in this area is reinforced. Owing to this cooling, the conventional problem of wear due to difference in thermal expansion between the fitting section of the member and the gas pass side flange end to be fitted is decreased, and the reliability of the tail tube seal structure is enhanced.
Further, the gas pass is generally in a cylindrical shape, and the inclined cooling holes are formed at specific intervals in the entire peripheral direction. Therefore, the inner wall of the gas pass can be cooled uniformly and efficiently also in the peripheral direction.
Further, the air flowing out from the inclined cooling holes flows smoothly along the inner wall of the gas pass side formed of a smooth curvature. Therefore, the film cooling effect is enhanced, and the cooling of the flange end at the gas pass side is further effective.
According to one aspect of the present invention, the seal member is fitted outside to the flange of the outer circumference of the tail tube outlet, and also fitted to the protrusion at the gas pass side on the outer periphery of the tail tube outlet wall. Therefore, the member itself does not come in contact with the high temperature combustion gas. Hence, it is not necessary to cool the member itself, and hence cooling holes and cooling are not needed. Instead, to reinforce cooling of the tail tube outlet wall, inclined cooling holes are provided around the tail tube outlet wall, and air is passed in the cooling holes to flow out in the gas passage to cool, and this cooling is a further addition to the conventional cooling of the tail tube wall inside. Therefore, in the present invention, the effect of the high temperature combustion gas in the tail tube seal is much smaller than in the prior art, and the consumption of cooling air is saved substantially.
Further, the seal member is placed in the fitting section between the tail tube outlet flange and the protrusion member at the gas pass side, the tail tube outlet peripheral flange end and the gas pass side protrusion are sealed securely, and the effect of the present invention is further encouraged.
Further, a brush seal is used. This brush seal seals by contacting with the smooth plane of the flange end of the gas pass side, and if a relative deviation occurs between the gas pass side flange end and the tail tube side, by sliding of the brush seal. Therefore, it is possible for the brush seal to move relatively depending on the deviation, and excessive force is not applied to the connection area, so that the reliability of the tail tube seal is enhanced.
Further, since a brush seal is used, in addition to the above effects, if a relative deviation occurs between the gas pass inlet side and the tail tube side, it is possible to move relatively, corresponding to this deviation, by sliding of the brush seal without spoiling the sealing performance, and excessive force is not applied to the connection area, so that the effects of the present invention may be assured.
Further, the shape of the inclined cooling holes is either circular or elliptical, and the hole shape can be selected depending on the type or structure of combustor, or by forming slender holes, the number of holes may be decreased, and the shape of the inclined cooling holes may be selected appropriately depending on the size or shape of the combustor, size at the gas pass side and other conditions, and the freedom of design is wider, which contributes to optimum designing.
According to still another aspect of the present invention, from the variety of tail tube seal structures exemplified herein, the best tail tube seal structure can be selected depending on the capacity or type of the gas turbine, and by using it, a gas turbine enhanced in the cooling effect in the tail tube seal, curtailed in the amount of cooling air, and enhanced in performance is realized.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.